Democrats started licking their chops moments after Republican presidential nominee Mitt Romney announced that he had selected Wisconsin Rep. Paul Ryan to be his running mate.

Whether the reaction came from the national party's House and Senate campaign committees, President Barack Obama's re-election campaign or individual Democratic campaigns around the country, the message was the same: Republicans want to end Medicare, and the issue will help Democrats define the terms of the 2012 elections.

But a month to the day after the Ryan announcement, it's hard to know the exact impact of the Medicare issue, particularly in House races. A few weeks from now, after individual Congressional contests have fully engaged over the issue and pollsters from both sides of the aisle have measured the impact, we'll have a better idea of how the issue is playing.

While Democrats have pounded on the topic since Ryan's selection, Republicans have not merely ducked and covered. Instead, they went on the offense, charging the president and his party with taking money from Medicare (to pay for health care reform) and putting the program in jeopardy.

Make no mistake about it: Medicare is a crucial political issue for Democrats running for the House and the Senate. They are relying on it heavily, though not exclusively, across the country to define GOP incumbents as insensitive to seniors and siding with millionaires over older Americans.

On Aug. 11, minutes after Romney introduced Ryan as his running mate aboard the USS Wisconsin, the Democratic Congressional Campaign Committee sent out an email titled "BREAKING - Congressman [John] Kline Has New Running Mate: Republican Budget That Ends Medicare."

The next day, a DCCC memo claimed "Ryan Budget Puts Republicans in Deep Jeopardy over Medicare," and two days later, the committee sent out a press release announcing "DCCC Launches New Advertising Linking 50 Republicans To Paul Ryan's Budget that Ends Medicare."

Not surprisingly, the DCCC's first independent expenditure TV ad of the cycle, aimed at Michigan Rep. Dan Benishek (R), accused him of supporting the privatization of Social Security and Medicare and of wanting to end Medicare.

Another DCCC ad charged New York Rep. Chris Gibson (R) with wanting "essentially to end Medicare." Both ads asserted that seniors would pay $6,400 a year more for health care, though only the Gibson spot specifically cited the Ryan budget.

Just recently, the DCCC unloaded on other Republicans using the issue, including incumbent Reps. Jeff Denham (Calif.) and Bobby Schilling (Ill.) and Illinois open-seat hopeful Jason Plummer.

Of course, where the DCCC has had a better opening attack against a Republican - for example, Rep. Brian Bilbray (Calif.) and Arizona candidate Jonathan Paton - the committee is using it in ads.

My initial assumption about the issue wasn't all that different from most observers. I knew Democrats would use the Ryan budget and Medicare even if he had not been added to the ticket, but I assumed that the selection of the Wisconsin lawmaker as Romney's running mate would make the issue even more salient and improve Democrats' chances in the 2012 elections.

But after speaking with a number of strategists and operatives, I'm not sure how the issue will shake out in November.

One veteran Democratic strategist surprised me recently by being skeptical that Medicare would be a winning issue for his party. The health care bill has changed how people, including seniors, feel about health care programs and costs, he argued. Things aren't as simple as they were in the late 1970s and 1980s, when Democrats used Social Security and Medicare so effectively in Congressional elections.

But another Democratic strategist argued that the issue is the best one that Democrats have, and insisted, "Yes, the Medicare message was stale [after being used for over three decades], but the Ryan plan and putting Ryan on the Republican ticket has refurbished it as an issue."

Republicans are also split on the issue.

An Aug. 23-24 auto-dial poll of 1,170 likely voters conducted for the National Republican Congressional Committee found more than 54 percent of respondents saying that they did not believe "Republicans want to end Medicare as we know it so they can give tax breaks to millionaires." And there are some Republicans who believe the Medicare issue has evolved over the years so that Americans now understand that doing nothing is not an alternative.

But plenty of Republicans remain very nervous about the issue. Few believe that it will be a winner for their candidates, and one GOP strategist worried that voters might well identify the GOP as the party most likely to cut Medicare, since Republicans have talked for years about cutting government programs and spending.

Mostly, Republicans simply are hoping that the partisan bickering over who did what to Medicare and which party wants to protect it will result in a wash, with neither party having a clear advantage.

While you can find poll numbers to prove whatever you want about Medicare, some things clearly are true. Most voters don't want to eliminate Medicare or replace the current system with a voucher. Given what they've heard, they oppose the Ryan approach to Medicare (Aug. 22-25 ABC News/Washington Post poll), and they also think that Medicare is extremely or very important to their "financial security in retirement" (a mid-August AP-GfK poll).

But the question is not merely whether voters like Medicare or support the Ryan budget. The question is whether, and how, the issue influences people's votes - and particularly the votes of seniors - in November.

If Medicare turns out to be the decisive issue that Democrats believe it will be, the fight for the House could get more interesting.

But if seniors conclude that their benefits are safe with Paul Ryan and people in their 40s and early 50s believe that doing nothing is a greater risk than adopting the Ryan plan, then the issue won't have nearly the bite - nor the electoral results - that Democrats now hope.